Introduction

This is a very simple picture viewer that illustrates some implementation details that you might want to use in your own Pocket PC 2002 projects. These are:

Using the imgdecmp.lib for loading BMP, JPEG and GIF image files.

Implementing a "tap-and-scroll" for scrolling convenience.

Implementing a full screen view.

Removing the "New" button from a Document / View toolbar.

Adding a title bar to the view (new)

Application architecture

This application uses the MFC's Document / View architecture in order to ease implementation. Bitmap pictures are drawn in a CScrollView-derived class, with a special support for the "tap-and-scroll" functionality. This allows the user to scroll the bitmap using the stylus, by tapping and dragging it. The document does not allow saving (after all, this is a viewer), but supports zooming. The zoom in and zoom out commands are supported at the document level although, arguably, they could be implemented at the view level.

Loading images

Images are loaded through a sparsely-documented API, implemented through the imgdecmp.lib. Both this library and its header are distributed with the PPC2002 SDK. Apparently, this is the same mechanism that is used by Pocket IE to load its images from the Internet, and that is why it supports a packet architecture. As for file formats, it is reported to support BMP, JPEG and GIF, but it may support more.

Images are loaded in CPicViewDoc::Serialize(). The process (see source) involves calling the DecompressImageIndirect() function, the DecompressImageInfo structure and two callback functions. The first callback function - GetImageData() - is used to read the image data in chunks, whereas the second - ImageProgress() - is used to report the image loading progress. In this sample, the callback does nothing (but yes, it must be there).

The fields of the DecompressImageInfo structure are quite self-explanatory, with one exception: lParam. This is the parameter that is passed to the callback functions, and I use it to carry a pointer to a structure containing a pair of values (ReadBmp): the CFile pointer retrieved from the open CArchive, and a counter of the image size. This is not strictly necessary for this application because one file has just one image, so passing the CFile* in lParam would be enough. This technique is used because it allows for extensibility, in the case where the file has multiple images, such as a skin file. Here you cannot rely in the end-of-file stop rendering the bitmap.

Tap-And-Scroll

This technique allows scrolling the image with a tap and drag sequence. The image will follow the stylus, scrolling automatically. The scroll bars are also present and active.

In order to achieve this effect, the view handles both OnLButtonDown() and OnMouseMove() (see code). The first stores the tap point, and the second calculates the scroll vector. This vector is then used in the ScrollTo() method, where the new scroll position is calculated. Note that this code was directly adapted from MFC's sources in order to avoid the unpleasant "jagged" scrolling one gets by using CScrollView::ScrollToPosition(). This method does not allow scrolling in both x and y directions simultaneously.

Full screen view

In the Pocket PC 2002, the full screen functionality is achieved through the SHFullScreen API. This function allows the application to position its main window over areas that are usually controlled by the system, such as the SIP and the taskbar. The code that achieves this is in the CMainFrame::OnFullScreen() handler. In order to support full screen toggling, a context menu is available through the tap-and-hold command. This menu allows you to enter and leave the full screen mode, as well as to issue Zoom In and Zoom Out commands.

Title bar

Updated on October 27, 2003. The sample application now supports a title bar for displaying the image's file name. This title bar can be hidden or shown via a menu option, under Tools.

This title bar is implemented through the CCeTitleBar class, a CControlBar-derived window. It merely displays the title text in a predefined font and color.

Using this class is very straightforward (see source code). The window is created on the view's OnCreate handler and destroyed in OnDestroy. The view's OnUpdate handler is used to set the title text (document file name). Showing and hiding the title bar is done in the view's OnShowTitle handler.

Comments and Discussions

If have one question. In my program, I load many pictures do show in a listview (thumbnails). The handle to the bitmap (HBITMAP) gets lost after drawing the picture. If the picture needs to be redrawn, it will be read again from the file.

So my question, before the handle is lost, do I need to free up the memory where the bitmap is stored?

I load the picture as shown in your example with help of DecompressImageIndirect:

...
dii.phBM = & hBmp;
...
hr = DecompressImageIndirect(& dii);
...

Then I use
dcMem.SelectObject(hBmp);
to draw the picture.

I don't want to save the picture in the memory after it has been drawn. So before loading the next picture (and of course before hBmp gets lost when leaving the function), I need to call
DeleteObject(hBmp);
Do I understand that right?

Hello...I am currently developing an application in evc 3.0 for a PDA(iPAQ) and I want this app and some folders related to it to stay in the device even if reset is done(which erases all the files loaded externally to it)!!

How can it be done??
Plzz help!!

Also another thing, if I want to protect some folders from user access, what should I do??

I am trying to implement the imgdecmp using Dialog-based mfc. Everything is fine, except that while the image is being displayed on the screen, then I click on start menu, or change the volume, the image is disappear.
How can I keep the image?

Sorry... this msg has nothing to do with the picture viewer... I just need some help on a similar issue of linking... I use evc++ 4.0 sp4. I get the following error while linking... I use win32(WCE x86) Debug and StandardSDK Emulator...